1. Field of the Invention
The present invention relates to a cam mechanism in which a cam is protruded from the surface and/or back of a gear, a cam apparatus utilizing the cam mechanism, and a mowing machine utilizing the cam apparatus.
2. Description of Related Art
Conventionally, a cam mechanism for converting the circular motion to the reciprocating motion is shown in FIG. 1A and FIG. 1B is known. The cam mechanism 100, as shown in FIG. 1A, comprises a gear 110 and a circular cam 120 fixed on the eccentric position of the gear 110. The gear 110 has a central hole 111 formed at the central position, and the circular cam 120 has an eccentric hole 121 having the same diameter as the diameter of the central hole 111 at the eccentric position. The circular cam 120 piles on the gear 110 and they are fixed together so that the center of the hole 111 is aligned to the center of the hole 121.
The circular cam 120 has two through holes 122 in the appropriate positions, and the gear 110 has screw holes 112 corresponding to the through holes 122. Then, as shown in FIG. 1B, the circular cam 120 is fixed to the gear 110 by inserting and screwing screws into the through holes 122 and the screw holes 112. It should be noted that the circular cam 120 may be fixed to the gear 110 by inserting and screwing caulking nails into the through holes 122 and the screw holes 112 instead of using the screws.
The gear 110 is supported by a supporting shaft 140 after the supporting shaft 140 is slidably inserted into the central hole 111 of the gear 110 and the eccentric hole 121 of the circular cam 120. The gear 110 engages with a driving gear 150, so that the gear 110 rotates around the supporting shaft 140 by the rotation of the driving gear 150 around a driving shaft 151.
As shown in FIG. 1B, there is a connecting rod 160 having a connecting hole 161 slidably fitted on the circular cam 120 of the cam mechanism 100. Accordingly, as the gear 110 rotates around the supporting shaft 140, the rotation is transmitted to the connecting rod 160 through the circular cam 120 eccentric-rotating around the supporting shaft 140, so that the connecting rod 160 reciprocates in the direction shown by the arrows in FIG. 1B.
The above-described cam mechanism 100 is utilized in the various kinds of apparatus which require the conversion of the circular motion into the reciprocating motion. For example, there are mowing machines for gardening disclosed in Japanese Patent Laid-open No. 64-41249, Japanese Patent Laid-open No. 60-137214 and Japanese Patent Laid-open No. 56-106512.
In the conventional cam mechanism 100 shown in FIGS. 1A, 1B, in order to make a circular cam 120 on the gear 110, first the circular cam 120 has to be manufactured individually, which makes the material cost and the manufacturing cost higher.
Further, the circular cam 120 is fixed on the gear 110 under the complicated steps in which the screw holes 112 are formed in the gear 110 and in which the through holes 122 are formed in the circular cam 120 corresponding to the screw holes 122 and in which screws 130 are inserted and screwed into the through holes 122 and the screw holes 112. This makes the assembling cost higher.
Therefore, it is an object of the present invention to provide a cam mechanism which can lower the manufacturing cost and the assembling cost, and a mowing machine utilizing the cam mechanism.
A cam mechanism of the present invention comprises a metal gear, and an eccentric cam protruded from the eccentric position of at least one of the surface and the back of the gear. The eccentric cam is formed by performing half blanking press processing on the gear from the other side of the eccentric cam to be formed.
The half blanking press processing is one of fine blanking.
The structure of the mold is either a zero clearance method in which no clearance exists between a blanking hole of a lower mold and a punch for blanking or a negative clearance method in which the cross section of the punch for blanking is slightly larger than the cross section of the blanking hole. The mold comprises a presser having a projection for pressing the material to be processed and an inverse presser for pressing the material from underneath. The material to be processed is pressed up to the half of the thickness while it is tightly held.
According to thus formed cam mechanism, the eccentric cam has an extremely smooth cut surface, no shear drop, no burr and the good dimensional accuracy. Therefore, the eccentric cam functions sufficiently when the circumferential surface slides to other member. Especially, with the employment of the negative clearance method, the dimensional accuracy of the eccentric cam is improved.
Further, the material cost and the processing cost are made lower as compared to the case that the eccentric cam is fixed to the gear with the screws or caulking, which mean that the manufacturing cost is lowered.
In the cam mechanism, the eccentric cam may be formed at the surface and back of the gear. Accordingly, the spur gear can convert the circular motion to the reciprocating motion at both surfaces.
Further, the gear may have a shaft hole at the central position, and the eccentric cams can be formed in point symmetry with respect to the axis of the shaft hole. Accordingly, a pair of other members can reciprocate in phase difference of 180 degrees.
Furthermore, the eccentric cam may comprise an inscribed surface inscribed in a circular locus having a center and a diameter so as to include the shaft hole, and a concave notch formed by separating an opposing surface which is the opposite side of the inscribed surface from the shaft hole by a predetermined distance.
Accordingly, when other member having a circular hole is fitted on the eccentric cam, the shaft inserted in the shaft hole of the gear is inserted in the circular hole, and a space is formed between the shaft and the concave portion of the eccentric cam. Therefore, the lubricant can be filled in the space, so that the eccentric cam can operate smoothly.
Further, in the case of the eccentric cams formed on the surface and back of the gear in point symmetry, although each circular locus interferes the other, the interference of the eccentric cams of the gear can be avoided because of the concave notch.
Furthermore, in the cam mechanism, a central shaft is inserted into the shaft hole, and a sliding ring is fitted on the central shaft, and the sliding ring has an outer diameter so as to slide on the inner surface of the shaft hole.
According to this cam mechanism, since the inner surface of other member is in contact with the outer surface of the central shaft over the sliding ring when other member having a circular hole is fitted on the eccentric cam, the gear rotates around the central shaft, which makes the crank motion of other member smoother.
Further, the eccentric cam may be formed by a plurality of cam protrusions inscribed in a circular locus having a center and a diameter so as to include the shaft hole. With the employment of the cam protrusions as the eccentric cam, total cross section of the plurality of protrusions is smaller than the cross section of the eccentric cam. Therefore, the press pressure of the half blanking press processing can be made smaller, which lowers the energy cost.
A cam apparatus of the present invention comprises one of the above-described cam mechanism of the present invention, and an output rod having a sliding hole at one end to fit slidably on the eccentric cam. The gear is connected to the output rod by fitting the sliding hole on the eccentric cam.
According to the cam apparatus, the rotation of the gear is converted into the reciprocating motion through the eccentric cam and the output rod.
A mowing machine of the present invention comprises one of the above-described cam mechanism of the present invention, and an output rod having a sliding hole at one end to fit slidably on the eccentric cam, to be connected to the output rod when the sliding hole is fitted on the eccentric cam, and a pair of blade members having a plurality of mowing blades. The mowing blades are piled up so as to be slidable in the lengthwise direction, and at least one of the pair of the blade members is connected to the other end of the output rod.
According to the mowing machine, the rotation of the gear is converted into the reciprocating motion through the eccentric cam and the output rod and transmitted to the pair of blade members. Then, the mowing blades reciprocate in the lengthwise direction to cut greens.